In recent years, in the technological fields of super computers or servers, a signal transmission rate between LSIs or between an LSI and a memory has been steadily accelerated. Due to the increase of the signal transmission rate, it is hard for the conventional electronic wiring systems to deal with problems such as degradation of signal waveforms and increase in power consumption. Currently, optical interconnections have been attracting attention as a new connection scheme to solve the problems. Optical interconnections are able to transmit a large number of signals at low power consumption using a broadband optical interconnect transmission path.
Inter-board connection using an optical interconnection between LSIs is realized by providing optical transmission paths such as optical fibers or optical waveguides between devices mounted on boards. Such devices include optical transmitter devices for converting electric signals to optical signals and optical receiver devices for converting optical signals to electric signals. To extend the hardware system or carry out maintenance for a supercomputer or server system with optical interconnects, an LSI-mounted board is removed from and inserted into the system. At this time, optical transmission paths are also disconnected from and connected to the system together with electric connectors adapted for power feeding or low-rate signal transmission. For this reason, in the field of optical interconnection, development of detachable fiber optic connectors are expected as well as development of optical devices and optical transmission lines.
The number of the optical transmission lines used as optical interconnections in a server system is enormous. Many inventions have been made for multi-fiber optical connectors for connecting multi-channel optical transmission paths mainly in the technological field of optical communications. In particular, MT-ferrule based optical connectors employing a mechanical splice technique are widely used at present. In the MT-ferrule based connectors, optical fibers are aligned at a predetermined pitch inside a ferrule. The optical fibers of two facing connectors are correctly positioned with respect to each other using a guide pin provided in one of the connectors and a guide hole provided in the other. Then the optical fibers of one connector are collectively brought into contact with the optical fibers of the counterpart connector when the two connectors are mated to each other.
However, constructing optical interconnections using MT-ferrule-based connectors adapted for optical communications purposes will lead to increase of the cost. This is because the end faces of optical fibers are polished at high precision after the optical fibers are incorporated into the ferrule to adjust the amount of projections of the fibers. To reduce the cost, no-polish connectors are preferred.
A method called high-speed MT connector assembly is known to implement a low-cost no-polish fiber connector. With this method, a jig with a slight recess is pushed against the front face of an MT ferrule when assembling optical fibers in the MT ferrule. Using this jig, the optical fibers can be incorporated in the MT ferrule with the ends projecting from the front face of the ferrule. However, it is difficult to precisely control the amount of projection of the optical fibers due to variation in the lengths of the optical fibers. In addition, some of the optical fibers do not project from the ferrule; rather, they are retracted inside the ferrule. If two optical connectors are mated to each other under the condition where fluctuations exist in the amount of fiber projection, an impulsive force is concentrated on the channel with a large amount of fiber projection. In this case, optical fibers are damaged and long-term reliability is not achieved.
To reduce the influence of the variation in the fiber projection, it is proposed to press a dummy ferrule against the end faces of the optical fibers to align the end position of the optical fibers (see, Patent Document 1 listed below). A method of applying an optically transparent resin to the front face of the ferrule is also proposed (see, Patent Document 2 listed below), where the index of refraction of the optically transparent resin is close to that of the optical fiber cores.
Optical connectors at low cost and high connection reliability are desired.                Patent Document 1: Japanese Laid-open Patent Publication No. 2001-228359        Patent Document 2: Japanese Laid-open Patent Publication No. 2002-31745        